Russel Lowe, a member of a local security company who was at the scene told The Citizen he received a message on his phone about the hold-up.
“I believe that two men were involved and one was armed with a pistol,” he said.
Pupils, parents and teachers were on the sport field enjoying a Heritage Day event when the men entered the administration block, said parent David van Rayne.
“The children had finished a fun run and we were waiting for the soccer team to come on to the field when we heard the news,” said Van Rayne.
Police were on scene and are investigating the matter. Nobody was hurt in the incident.